1. Field of the Invention
The present invention relates to an electrical circuit for supplying high-voltage AC electrical energy to and for regulating resistive current through a complex load; and, more particularly, to such a circuit including a voltage controlled inverter and having means for compensating for variations in load current resulting when a changing characteristic of the complex load causes variations in the ratio of peak to average rectified resistive current to the complex load.
2. Description of the Prior Art
The present invention was conceived as an improvement upon the electrical circuit having means for regulating resistive current through a complex load set forth in the copending application of William R. Archer, Ser. No. 042,765, filed May 29, 1979, and assigned to General Electric Company, the assignee of the present invention.
A high-voltage AC power supply such as that described and claimed in the Archer application is capable, with modification, of providing an output voltage waveform of the type shown in FIGS. 2 and 4. Such a high-voltage AC power supply may be used to supply a non-linear complex load, such as for example, a corotron of the type used in reprographic equipment and having the characteristic shown in FIG. 3. One requirement of such a power supply is that the average rectified resistive current be regulated and held constant as the load characteristic of the corotron changes from condition "a" to condition "b" as seen in FIG. 3. The Archer application describes a regulation scheme which senses the output current during the flat top period of the output waveform, and then controls the output voltage so as to maintain a constant peak to peak resistive component of output current.
It was discovered, however, that simply regulating the peak to peak value of output current does not result in a regulated rectified resistive average current because the peak current value duty cycle of the resistive current changes when the corotron load characteristic changes from condition "a" to condition "b." In other words, the ratio of peak to average rectified resistive load current does not remain constant when the load characteristic of a complex load changes.
This duty cycle or waveform change in the resistive load current is also shown in FIG. 4. It can be seen that, if the peak value of resistive load current is maintained constant (regulated), then the average rectified value thereof, the area under the current waveform curve, will be a smaller value at the higher output voltage condition "b. " In order to correct for such a condition, a higher peak current is needed in condition "b."
It was also recognized that the effects of a voltage divider used in a feedback circuit to conrol the inverter also has a bearing on regulating the output current. Such a voltage divider is placed in parallel with the complex load across the output of the voltage controlled inverter. A sense resistor used in the current regulation scheme senses both the divider current and output load current. If the current as sensed by the sense resistor is regulated to maintain a constant value, then, at the higher output voltage condition, a greater amount of current will be flowing in the divider and less in the load. To compensate for this condition, it would also be necessary to provide more output current, that is more peak current, in load condition "b" of FIG. 4, the higher output voltage condition.
It is desirable to provide a high-voltage AC power supply for driving a complex load which is capable of compensating for both the above-mentioned effects thereby to result in a power supply with improved regulation characteristics.
It is, therefore, an object of the present invention to provide a high-voltage AC power supply which is capable of providing a regulated rectified average resistive current to compensate for changes in the characteristic of the complex load and at the same time to compensate for the effects of this voltage divider placed in parallel with the complex load across the output of the power supply.